Hydrocarbon dehydrogenation with an attenuated superactive multimetallic catalytic composite for use therein

ABSTRACT

Dehydrogenatable hydrocarbons are dehydrogenated by contacting them, at hydrocarbon dehydrogenation conditions, with a novel attenuated superactive multimetallic catalytic composite comprising a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of catalytically effective amounts of a platinum group component maintained in the elemental metallic state, and of a manganese component. An example of the attenuated superactive nonacidic multimetallic catalytic composite disclosed herein is a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of catalytically effective amounts of an alkali or alkaline earth component, a manganese component, and of a platinum group component which is maintained in the elemental metallic state during the incorporation of a rhenium carbonyl component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of my prior, copendingapplication Ser. No. 46,885 filed June 8, 1979 and issued on Dec. 9,1980 as U.S. Pat. No. 4,238,366; which in turn is a division of my priorapplication Ser. No. 943,492 filed Sept. 18, 1978 and issued Jan. 15,1980 as U.S. Pat. No. 4,183,805; which in turn is a continuation-in-partof my prior application Ser. No. 833,332 filed Sept. 14, 1977 and issuedAug. 21, 1979 as U.S. Pat. No. 4,165,276. All of the teachings of theseprior applications are specifically incorporated herein by reference.

The subject of the present invention is, broadly, an improved method fordehydrogenating a dehydrogenatable hydrocarbon to produce a hydrocarbonproduct containing the same number of carbon atoms but fewer hydrogenatoms. In another aspect, the present invention involves a method ofdehydrogenating normal paraffin hydrocarbons containing 3 to 30 carbonatoms per molecule to the corresponding normal mono-olefin with minimumproduction of side products. In yet another apsect, the presentinvention relates to a novel attenuated superactive nonacidicmultimetallic catalytic composite comprising a combination of acatalytically effective amounts of a pyrolyzed rhenium carbonylcomponent with a porous carrier material containing a uniform dispersionof catalytically effective amount of an alkali or alkaline earthcomponent, a manganese component, and a platinum group component whichis maintained in the elemental metallic state. This non-acidic compositehas highly beneficial characteristics of activity, selectivity, andstability when it is employed in the dehydrogenation of dehydrogenatablehydrocarbons such as aliphatic hydrocarbons, naphthene hydrocarbons, andalkylaromatic hydrocarbons.

The conception of the present invention followed from my search for anovel catalytic composite possessing a hydrogenation-dehydrogenationfunction, a controllable cracking function, and superior conversion,selectivity, and stability characteristics when employed in hydrocarbonconversion processes that have traditionally utilized dual-functioncatalytic composites. In my prior application Ser. No. 943,492, now U.S.Pat. No. 4,183,805 I disclosed a significant finding with respect to amultimetallic catalytic composite meeting these requirements. Morespecifically, I determined that a pyrolyzed rhenium carbonyl componentcan be utilized, under certain specified conditions, to beneficiallyinteract with the platinum group and manganese components of adual-function catalyst with a resulting marked improvement in theperformance of such a catalyst. Now I have ascertained that a catalyticcomposite, comprising a combination of catalytically effective amountsof a platinum group component, a pyrolyzed rhenium carbonyl componentand a manganese component with a porous carrier material can havesuperior activity, selectivity and stability characteristics when it isemployed in a hydrocarbon dehydrogenation process if these componenetsare uniformly dispersed in the porous carrier material in the amountsspecified hereinafter and if the oxidation state of the platinum groupcomponent is carefully controlled so that substantially all of thiscomponent is present in the elemental metallic state during theincorporation of the rhenium carbonyl component. I have discerned,moreover, that a particularly preferred attenuated multimetalliccatalytic composite of this type contains not only a platinum groupcomponent, a manganese component, and a pyrolyzed rhenium carbonylcomponent, but also an alkali or alkaline earth component in an amountsufficient to ensure that the resulting catalyst is nonacidic.

The dehydrogenation of dehydrogenatable hydrocarbons is an importantcommercial process because of the great and expanding demand fordehydrogenated hydrocarbons for use in the manufacture of variouschemical products, such as detergents, plastics, synthetic rubbers,pharmaceutical products, high octane gasolines, perfumes, drying oils,ion-exchange resins, and various other products well known to thoseskilled in the art. One example of this demand is in the manufacture ofhigh octane gasoline by using C₃ and C₄ mono-olefins to alkylateisobutane. Another example of this demand is in the area ofdehydrogenation of normal paraffin hydrocarbons to produce normalmono-olefins having 3 to 30 carbon atoms per molecule. These normalmono-olefins, can, in turn, be utilized in the synthesis of a vastnumber of other chemical products. For example, derivatives of normalmono-olefins have become of substantial importance to the detergentindustry where they are utilized to alkylate an aromatic, such asbenzene, with subsequent transformation of the product arylalkane into awide variety of biodegradable detergents such as alkylaryl sulfonatetypes of detergents which are most widely used today for household,industrial, and commercial purposes. Still another large class ofdetergents produced from these normal mono-olefins are the oxyalkylatedphenol derivatives in which the alkylphenol base is prepared by thealkylation of phenol with these normal mono-olefins. Still another typeof detergent produced from these normalmono-olefins are thebiodegradable alkylsulfonates formed by the direct sulfation of thenormal mono-olefins. Likewise, the olefin can be subjected to directsulfonation with sodium bisulfite to make biodegradable alkysulfonates.As a further example, these mono-olefins can be hydrated to producealcohols which then, in turn, can be used to produce plasticizers and/orsynthetic lube oils.

Regarding the use of products made by the dehydrogenation ofalkylaromatic hydrocarbons, they find wide application in the petroleum,petrochemical, pharmaceutical, detergent, plastic, and the likeindustries. For example, ethylbenzene is dehydrogenated to producestyrene which is utilized in the manufacture of polystyrene plastics,styrene-butadiene rubber, and the like products. Isopropylbenzene isdehydrogenated to form alpha-methyl styrene which, in turn, isextensively used in polymer formation and in the manufacture of dryingoils, ion-exchange resins, and the like materials.

Responsive to this demand for these dehydrogenation products, the arthas developed a number of alternative methods to produce them incommercial quantities. One method that is widely utilized involves theselective dehydrogenation of a dehydrogenatable hydrocarbon bycontacting the hydrocarbon with a suitable catalyst at dehydrogenationconditions. As is the case with most catalytic procedures, the principalmeasure of effectiveness for this dehydrogenation method involves theability of the catalyst to perform its intended function with minimuminterference of side reactions for extended periods of time. Theanalytical terms used in the art to broadly measure how well aparticular catalyst performs its intended functions in a particularhydrocarbon conversion reaction are activity, selectivity, andstability, and for purposes of discussion here, these terms aregenerally defined for a given reactant as follows: (1) activity is ameasure of the catalyst's ability to convert the hydrocarbon reactantinto products at a specified severity level where severity level meansthe specific reaction conditions used--that is, the temperature,pressure, contact time, and presence of diluents such as H₂ ; (2)selectivity usually refers to the amount of desired product or productsobtained relative to the amount of the reactant charged or converted;(3) stability refers to the rate of change with time of the activity andselectivity parameters--obviously, the smaller rate implying the morestable catalyst. In a dehydrogenation process, more specifically,activity commonly refers to the amount of conversion that takes placefor a given dehydrogenatable hydrocarbon at a specified severity leveland is typically measured on the basis of disappearance of thedehydrogenatable hydrocarbon; selectivity is typically measured by theamount, calculated on a mole or weight percent of converteddehydrogenatable hydrocarbon basis, of the desired dehydrogenatedhydrocarbon obtained at the particular activity or severity level; andstability is typically equated to the rate of change with time ofactivity as measured by disappearance of the dehydrogenatablehydrocarbon and of selectivity as measured by the amount of desireddehydrogenated hydrocarbon produced. Accordingly, the major problemfacing workers in the hydrocarbon dehydrogenation art is the developmentof a more active and selective catalytic composite that has goodstability characteristics.

I have now found an attenuated superactive multimetallic catalyticcomposite which possesses improved activity, selectivity, and stabilitywhen it is employed in a process for the dehydrogenation ofdehydrogenatable hydrocarbons. In particular, I have determined that theuse of an attenuated superactive multimetallic catalyst, comprising acombination of catalytically effective amounts of a platinum groupcomponent, a pyrolyzed rhenium carbonyl component and a manganesecomponent with a porous refractory carrier material, can enable theperformance of a hydrocarbon dehydrogenation process to be substantiallyimproved if the platinum group component is uniformly dispersedthroughout the carrier material prior to incorporation of the rheniumcarbonyl component, if the oxidation state of the platinum groupcomponent is maintained in the elemental metallic state prior to andduring contact with the rhenium carbonyl component and if hightemperature treatments in the presence of oxygen and/or water of thereaction product of the rhenium carbonyl with the carrier materialcontaining the platinum group component is avoided. Moreover,particularly good results are obtained when this composite is combinedwith an amount of an alkali or alkaline earth component sufficient toensure that the resulting catalyst is nonacidic and utilized to producedehydrogenated hydrocarbons containing the same carbon structure as thereactant hydrocarbon but fewer hydrogen atoms. This nonacidic compositeis particularly useful in the dehydrogenation of long chain normalparaffins to produce the corresponding normal mon-olefin withminimization of side reactions such as skeletal isomerization,aromatization, cracking and polyolefin formation. In sum, the presentinvention involves the significant finding that a pyrolyzed rheniumcarbonyl component can be utilized under the circumstances specifiedherein to beneficially interact with and promote a hydrocarbondehydrogenation catalyst containing a platinum group metal andmanganese.

It is accordingly, one object of the present invention to provide anovel method for the dehydrogenation of dehydrogenatable hydrocarbonsutilizing an attenuated superactive multimetallic catalytic compositecomprising catalytically effective amounts of a platinum groupcomponent, a pyrolyzed rhenium carbonyl component, and a manganesecomponent combined with a porous carrier material. A second object is toprovide a novel nonacidic catalytic composite having superiorperformance characteristics when utilized in a hydrocarbondehydrogenation process. Another object is to provide an improved methodfor the dehydrogenation of normal paraffin hydrocarbons to producenormal mono-olefins, which method minimizes undesirable side reactionssuch as cracking, skeletal isomerization, polyolefin formation,disproportionation and aromatization.

In brief summary, one embodiment of the present invention involves amethod for dehydrogenating a dehydrogenatable hydrocarbon whichcomprises contacting the hydrocarbon at hydrocarbon dehydrogenationconditions with an attenuated superactive multimetallic catalyticcomposite comprising a porous carrier material containing a uniformdispersion of catalytically effective and available amounts of aplatinum group component, a manganese component and of a pyrolyzedrhenium carbonyl component. Substantially all of the platinum groupcomponent is, moreover, present in the composite in the elementalmetallic state during the incorporation of the rhenium carbonylcomponent and the pyrolysis of the rhenium carbonyl component isperformed after it has been reacted with the porous carrier materialcontaining the platinum group and manganese components. Further, thesecomponents are preferably present in this composite in amounts,calculated on an elemental basis, sufficient to result in the compositecontaining about 0.01 to about 2 wt. % platinum group metal, about 0.01to about 5 wt. % rhenium derived from the rhenium carbonyl component,and about 0.01 to about 5 wt. % manganese, and this composite ispreferably maintained in a substantially halogen-free state during usein the dehydrogenation method.

A second embodiment relates to the dehydrogenation method described inthe first embodiment wherein the dehydrogenatable hydrocarbon is analiphatic compound containing 2 to 30 carbon atoms per molecule.

A third embodiment comprehends an attenuated superactive nonacidiccatalytic composite comprising a porous carrier material havinguniformly dispersed therein catalytically effective and availableamounts of a platinum group component, a pyrolyzed rhenium carbonylcomponent, a manganese component, and an alkali or alkaline earthcomponent. These components are preferably present in amounts sufficientto result in the catalytic composite containing, on an elemental basis,about 0.01 to about 2 wt. % platinum group metal, about 0.01 to about 5wt. % manganese, about 0.1 to about 5 wt. % alkali metal or alkalineearth metal and about 0.01 to about 5 wt. % rhenium, derived from therhenium carbonyl component. In addition, substantially all of theplatinum group component is present in the elemental metallic stateduring incorporation of the rhenium carbonyl component, the pyrolysis ofthe rhenium carbonyl component occurs after combustion thereof with theporous carrier material containing the platinum group and manganesecomponents and substantially all of the alkali or alkaline earthcomponent is present in an oxidation state above that of the elementalmetal.

Another embodiment pertains to a method for dehydrogenating adehydrogenatable hydrocarbon with comprises contacting the hydrocarbonwith the nonacidic catalytic composite described in the third embodimentat dehydrogenation conditions.

Other objects and embodiments of the present invention involve specificdetails regarding essential and preferred catalytic ingredients,preferred amounts of ingredients, suitable methods of multimetalliccomposite preparation, suitable dehydrogenatable hydrocarbons, operatingconditions for use in the dehydrogenation process, and the likeparticulars. These are hereinafter given in the following detaileddiscussion of each of these facets of the present invention. It is to beunderstood that (1) the term "nonacidic" means that the catalystproduces less than 10% conversion of 1-butene to isobutylene when testedat dehydrogenation conditions and, preferably, less than 1%; (2) theexpression "uniformly dispersed throughout the carrier material" isintended to mean that the amount of the subject component, expressed ona weight percent basis, is approximately the same in any reasonablydivisible portion of the carrier material as it is in gross; and (3) theterm "substantially halogen-free" means that the total amount of halogenpresent in the catalytic composite in any form is less than about 0.2wt. %, calculated on an elemental basis.

Regarding the dehydrogenatable hydrocarbon that is subjected to themethod of the present invention, it can, in general, be an organiccompound having 2 to 30 carbon atoms per molecule and containing atleast one pair of adjacent carbon atoms having hydrogen attachedthereto. That is, it is intended to include within the scope of thepresent invention, the dehydrogenation of any organic compound capableof being dehydrogenated to produce products containing the same numberof carbon atoms but fewer hydrogen atoms, and capable of being vaporizedat the dehydrogenation temperature used herein. More particularly,suitable dehydrogenatable hydrocarbons are: aliphatic hydrocarbonscontaining 2 to 30 carbon atoms per molecule, alkylaromatic hydrocarbonswhere the alkyl group contains 2 to 6 carbon atoms, and naphthenes oralkyl-substituted naphthenes. Specific examples of suitabledehydrogenatable hydrocarbons are: (1) alkanes such as ethane, propane,n-butane, isobutane, n-pentane, isopentane, n-hexane, 2-methylpentane,3-methylpentane, 2,2-dimethylbutane, n-heptane, 2-methylhexane,2,2,3-trimethylbutane, and the like compounds; (2) naphthenes such ascyclopentane, cyclohexane, methylcyclopentane, ethylcyclopentane,n-propylcyclopentane, 1,3-dimethylcyclohexane, and the like compounds;and (3) alkylaromatics such as ethylbenzene, n-butylbenzene,1,3,5-triethylbenzene, isopropylbenzene, isobutylbenzene,ethylnaphthalene, and the like compounds.

In a preferred embodiment, the dehydrogenatable hydrocarbon is a normalparaffin hydrocarbon having about 3 to 30 carbon atoms per molecule. Forexample, normal paraffin hydrocarbons containing about 10 to 18 carbonatoms per molecule are dehydrogenated by the subject method to producethe corresponding normal mono-olefin which can, in turn, be alkylatedwith benzene and sulfonated to make alkylbenzene sulfonate detergentshaving superior biodegradability. Likewise, n-alkanes having 10 to 18carbon atoms per molecule can be dehydrogenated to the correspondingnormal mono-olefin which, in turn, can be sulfonated or sulfated to makeexcellent detergents. Similarly, n-alkanes having 6 to 10 carbon atomscan be dehydrogenated to form the corresponding mono-olefin which can,in turn, be hydrated to produce valuable alcohols. Preferred feedstreams for the manufacture of detergent intermediates contain a mixtureof 4 or 5 adjacent normal paraffin homologues such as C₁₀ to C₁₃, C₁₁ toC₁₄, C₁₁ to C₁₅ and the like mixtures. In an especially preferredembodiment, the charge stock to the present method is substantially purepropane.

The attenuated superactive multimetallic catalyst used in the presentinvention comprises a porous carrier material or support having combinedtherewith a uniform dispersion of catalytically effective amounts of aplatinum group component, a pyrolyzed rhenium carbonyl component, amanganese component, and, in the preferred case, an alkali or alkalineearth component.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon dehydrogenation process, andit is intended to include within the scope of the present inventioncarrier materials which have traditionally been utilized indual-function hydrocarbon conversion catalysts such as: (1) activatedcarbon, coke, or charcoal; (2) silica or silica gel, silicon carbide,clays, and silicates including those synthetically prepared andnaturally occurring, which may or may not be acid treated, for example,attapulgus clay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc.; (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, magnesia, boria, thoria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, CaAl₂ O₄, and other like compounds having the formula MO--Al₂ O₃where M is a metal having a valence of 2; and (7) combinations ofelements from one or more of these groups. The preferred porous carriermaterials for use in the present invention are refractory inorganicoxides, with best results obtained with an alumina carrier material.Suitable alumina materials are the crystalline aluminas known as gamma-,eta-, and theta-alumina, with gamma- or eta-alumina giving best results.In addition, in some embodiments the alumina carrier material maycontain minor proportions of other well-known refractory inorganicoxides such as silica, zirconia, magnesia, etc.; however, the preferredsupport is substantially pure gamma- or eta-alumina. Preferred carriermaterials have an apparent bulk density of about 0.2 to about 0.8 g/ccand surface area characteristics such that the average pore diameter isabout 20 to 300 Angstroms (B.E.T.), the pore volume is about 0.1 toabout 1 cc/g (B.E.T.) and the surface area is about 100 to about 500 m²/g (B.E.T.). In general, best results are typically obtained with asubstantially halogen-free gamma-alumina carrier material which is usedin the form of spherical particles having a relatively small diameter(i.e. typically about 1/16 inch), an apparent bulk density of about 0.2to about 0.8 g/cc, a pore volume of about 0.3 to about 0.8 cc/g(B.E.T.), and a surface area of about 125 to about 250 m² /g (B.E.T.).

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or naturally occurring.Whatever type of alumina is employed, it may be activated prior to useby one or more treatments including drying, calcination, steaming, etc.,and it may be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, tablets, etc., and utilized in anydesired size. For the purpose of the present invention a particularlypreferred form of alumina is the sphere, and alumina spheres may becontinuously manufactured by the well-known oil drop method whichcomprises: forming an alumina hydrosol by any of the techniques taughtin the art and preferably by reacting aluminum metal with hydrochloricacid, combining the resultant hydrosol with a suitable gelling agent anddropping the resultant mixture into an oil bath maintained at elevatedtemperatures. The droplets of the mixture remain in the oil bath untilthey set and form hydrogel spheres. The spheres are then continuouslywithdrawn from the oil bath and typically subjected to specific agingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° F.to about 400° F. and subjected to a calcination procedure at atemperature of about 850° F. to about 1300° F. for a period of about 1to about 20 hours. It is a good practice to subject the calcinedparticles to a high temperature treatment with steam in order to removeundesired acidic components such as residual chlorine and therebyprepare the preferred substantially halogen-free carrier material. Thispreparation procedure effects conversion of the alumina hydrogel to thecorresponding crystalline gamma-alumina. See the teachings of U.S. Pat.No. 2,620,314 for additional details.

Another particularly preferred alumina carrier material is synthesizedfrom a unique crystalline alumina powder which has been characterized inU.S. Pat. Nos. 3,852,190 and 4,012,313 as a by-product from a Zieglerhigher alcohol synthesis reaction as described in Zeigler's U.S. Pat.No. 2,892,858. For purposes of simplification, the name "Ziegleralumina" is used herein to identify this material. It is presentlyavailable from the Conoco Chemical Division of Continental Oil Companyunder the trademark Catapal. This material is an extremely high purityalpha-alumina monohydrate (boehmite) which after calcination at a hightemperature has been shown to yield a high purity gamma-alumina. It iscommercially available in three forms: (1) Catapal SB--a spray driedpowder having a typical surface area of 250 m² /g; (2) Catapal NG--arotary kiln dried alumina having a typical surface area of 180 m² /g;and (3) Dispal M--a finely divided dispersable product having a typicalsurface area of about 185 m² /g. For purposes of the present invention,the preferred starting material is the spray dried powder, Catapal SB.This alpha-alumina monohydrate powder may be formed into a suitablecatalyst material according to any of the techniques known to thoseskilled in the catalyst carrier material forming art. Spherical carriermaterial particles can be formed, for example, from this Ziegler aluminaby: (1) converting the alpha-alumina monohydrate powder into an aluminasol by reaction with a suitable peptizing acid and water and thereafterdropping a mixture of the resulting sol and a gelling agent into an oilbath to form spherical particles of an alumina gel which are easilyconverted to a gamma-alumina carrier material by known methods; (2)forming an extrudate from the powder by established methods andthereafter rolling the extrudate particles on a spinning disc untilspherical particles are formed which can then be dried and calcined toform the desired particles of spherical carrier material; and (3)wetting the powder with a suitable peptizing agent and thereafterrolling particles of the powder into spherical masses of the desiredsize in much the same way that children have been known to make parts ofsnowmen by rolling snowballs down hills covered with wet snow. Thealumina powder can also be formed in any other desired shape or type ofcarrier material known to those skilled in the art such as rods, pills,pellets, tablets, granules, extrudates and the like forms by methodswell-known to the practitioners of the catalyst carrier material formingart. The preferred type of carrier material for the present invention isa cylindrical extradate having a diameter of about 1/32 " to about 1/8"(especially about 1/16") and a length to diameter (L/D) ratio of about1:1 to about 5:1, with a L/D ratio of about 2:1 being especiallypreferred. The especially preferred extrudate form of the carriermaterial is preferably prepared by mixing the alumina powder with waterand a suitable peptizing agent such as nitric acid, acetic acid,aluminum nitrate and the like material until an extrudable dough isformed. The amount of water added to form the dough is typicallysufficient to give a loss on ignition (LOI) at 500° C. of about 45 to 65wt.%, with a value of about 55 wt.% being especially preferred. On theother hand, the acid addition rate is generally sufficient to provideabout 2 to 7 wt.% of the volatile free alumina powder used in the mix,with a value of about 3 to 4% being especially preferred. The resultingdough is then extruded through a suitably sized die to form extrudateparticles. It is to be noted that it is within the scope of the presentinvention to treat the resulting dough with an aqueous alkaline reagentsuch as an aqueous solution of ammonium hydroxide in accordance with theteachings of U.S. Pat. No. 3,661,805. This treatment may be performedeither before or after extrusion, with the former being preferred. Theseparticles are then dried at a temperature of about 500° to 800° F. for aperiod of about 0.1 to about 5 hours and thereafter calcined at atemperature of about 900° F. to about 1500° F. for a period of about 0.5to about 5 hours to form the preferred extrudate particles of theZiegler alumina carrier material. In addition, in some embodiments ofthe present invention the Ziegler alumina carrier material may containminor proportions of other well-known refractory inorganic oxides suchas silica, titanium dioxide, zirconium dioxide, chromium oxide,beryllium oxide, vanadium oxide, cesium oxide, hafnium oxide, zincoxide, iron oxide, cobalt oxide, magnesia, boria, thoria, and the likematerials which can be blended into the extrudable dough prior to theextrusion of same. In the same manner crystalline zeoliticaluminosilicates such as naturally occurring or synthetically preparedmordenite and/or faujasite, either in the hydrogen form or in a formwhich has been treated with a multivalent cation, such as a rare earth,can be incorporated into this carrier material by blending finelydivided particles of same into the extrudable dough prior to extrusionof same. A preferred carrier material of this type is a substantiallyhalogen-free and substantially pure Ziegler alumina having an apparentbulk density (ABD) of about 0.4 to 1 g/cc (especially an ABD of about0.5 to about 0.85 g/cc), a surface area (B.E.T.) of about 150 to about280 m² /g (preferably about 185 to about 235 m² /g) and a pore volume(B.E.T.) of about 0.3 to about 0.8 cc/g.

A first essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof as afirst component of the superactive catalytic composite. It is anessential feature of the present invention that substantially all ofthis platinum group component is uniformly dispersed throughout theporous carrier material in the elemental metallic state prior to theincorporation of the rhenium carbonyl ingredient. Generally, the amountof this component present in the form of catalytic composites is smalland typically will comprise about 0.01 to about 2 wt.% of finalcatalytic composite, calculated on an elemental basis. Excellent resultsare obtained when the catalyst contains about 0.05 to about 1 wt.% ofplatinum, iridium, rhodium or palladium metal. Particularly preferredmixtures of these platinum group metals preferred for use in thecomposite of the present invention are: (1) platinum and iridium and (2)platinum and rhodium.

This platinum group component may be incorporated in the porous carriermaterial in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion-exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium sulfate, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium or sodium chloroiridate, potassiumrhodium oxalate, etc. The utilization of a platinum, iridium, rhodium,or palladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is ordinarilypreferred. Nitric acid or the like acid is also generally added to theimpregnation solution in order to further facilitate the uniformdistribution of the metallic components throughout the carrier material.In addition, it is generally preferred to impregnate the carriermaterial after it has been calcined in order to minimize the risk ofwashing away the valuable platinum group component.

A second essential constituent of the multimetallic catalyst of thepresent invention is a manganese component. The component may in generalbe present in the instant catalytic composite in any catalyticallyavailable form such as a compound like the oxide, hydroxide, halide,oxyhalide, aluminate, or in chemical combination with one or more of theother ingredients of the catalyst. Although it is not intended torestrict the present invention by this explanation, it is believed thatbest results are obtained when the manganese component is present in thecomposite in a form wherein substantially all of the manganese moiety isin an oxidation state above that of the elemental metal such as in theform of manganese oxide or manganese aluminate, or a mixture thereof,and the subsequently described oxidation and reduction steps that arepreferably used in the preparation of the instant catalytic compositeare specifically designed to achieve this end. The term "manganesealuminate" as used herein refers to a coordinated complex of manganese,oxygen, and aluminum which are not necessarily present in the samerelationship for all cases covered herein. This manganese component canbe used in any amount which is catalytically effective, with goodresults obtained, on an elemental basis, with about 0.01 to about 5 wt.%manganese in the catalyst. Best results are ordinarily achieved withabout 0.05 to about 1 wt.% manganese, calculated on an elemental basis,and with an atomic ratio of manganese to platinum group metal of about0.1:1 to about 10:1, especially about 0.2:1 to about 3:1.

This manganese component may be incorporated into the porous carriermaterial in any suitable manner known to the art to result in arelatively uniform dispersion of the manganese moiety in the carriermaterial, such as by coprecipitation or cogellation or coextrusion withthe porous carrier material, ion exchange with the gelled carriermaterial, or impregnation with the carrier material either after,before, or during the period when it is dried and calcined. It is to benoted that it is intended to include within the scope of the presentinvention all conventional methods for incorporating and simultaneouslyuniformly distributing a metallic component in a catalytic composite andthe particular method of incorporation used is not deemed to be anessential feature of the present invention. One preferred method ofincorporating the manganese component into the porous carrier materialinvolves cogelling or coprecipitating or coextruding the manganesecomponent in the form of the corresponding hydrous oxide during thepreparation of the preferred carrier material, alumina. This methodtypically involves the addition of a suitable sol-soluble orsol-dispersable manganese compound such as manganese (II) chloride,nitrate, or acetate or permanganic acid to the alumina hydrosol and thencombining the hydrosol with a suitable gelling agent and forming theresulting mixture into particles of appropriate size and shape such asby dropping the resulting mixture into an oil bath, etc., as explainedin detail hereinbefore. Alternatively, the manganese compound can beadded to the gelling agent. After drying and calcining the resultinggelled carrier material in air, there is obtained an intimatecombination of alumina and manganese oxide and/or aluminate. Anotherpreferred method of incorporating the manganese component into theporous carrier material involves utilization of a soluble, decomposablecompound of manganese to impregnate the porous carrier material. Ingeneral, the solvent used in this impregnation step is selected on thebasis of the capability to dissolve the desired manganese compoundwithout adversely affecting the carrier material or the otheringredients of the catalyst--for example, a suitable alcohol, ether,acid and the like solvents. The solvent is preferably an aqueous acidicsolution. Thus, the manganese component may be added to the carriermaterial by commingling the latter with an aqueous acidic solution ofsuitable manganese salt, complex, or compound such as (1) manganese (II)acetate, bromide, chloride, formate, iodide, nitrate, lactate, and thelike salts, and (2) permanganic acid and salts thereof, (3) manganese(VII) oxide, and the like compounds. A particularly preferredimpregnation solution comprises an acidic aqueous solution ofpermanganic acid or manganese (II) nitrate. Suitable acids for use inthe impregnation solution are: inorganic acids such as hydrochloricacid, nitric acid, and the like, and strongly acidic organic acids suchas oxalic acid, malonic acid, citric acid, and the like. In general, themanganese component can be impregnated either prior to, simultaneouslywith, or after the platinum group component is added to the carriermaterial. However, excellent results are obtained when the manganesecomponent is added prior to the addition of the platinum groupcomponent.

A highly preferred optional ingredient of the catalyst used in thepresent invention is an alkali or alkaline earth component. Morespecifically, this component is selected from the group consisting ofthe compounds of the alkali metals--cesium, rubidium, potassium, sodium,and lithium--and of the alkaline earth metals--calcium, strontium,barium, and magnesium. This component exists within the catalyticcomposite in an oxidation state above that of the elemental metal as arelatively stable compound such as the oxide or hydroxide, or incombination with one or more of the other components of the composite,or in combination with the carrier material such as, for example, in theform of an alkali or alkaline earth metal aluminate. Since, as isexplained hereinafter, the composite containing the alkali or alkalineearth component is always calcined or oxidized in an air atmospherebefore use in the dehydrogenation of hydrocarbons, the most likely statethis component exists in during use in the dehydrogenation reaction isthe corresponding metallic oxide such as lithium oxide, potassium oxide,sodium oxide, and the like. Regardless of what precise form in which itexists in the composite, the amount of this component utilized ispreferably selected to provide a nonacidic composite containing about0.1 to about 5 wt.% of the alkali metal or alkaline earth metal, and,more preferably, about 0.25 to about 3.5 wt.%. Best results are obtainedwhen this component is a compound of lithium or potassium. The functionof this component is to neutralize any of the acidic material such ashalogen which may have been used in the preparation of the presentcatalyst so that the final catalyst is nonacidic.

The alkali or alkaline earth component may be combined with the porouscarrier material in any manner known to those skilled in the art toresult in a relatively uniform dispersion of this component throughoutthe carrier material with consequential neutralization of any acidicsites which may be present therein. Typically good results are obtainedwhen it is combined by impregnation, coprecipitation, ion-exchange, andthe like procedures. The preferred procedure, however, involvesimpregnation of the carrier material either before, during or after itis calcined, or before, during or after the other metallic ingredientsare added to the carrier material. Best results are ordinarily obtainedwhen this component is added to the carrier material simultaneously withor after the platinum group component and cadmium component, and beforethe rhenium carbonyl component because the alkali metal or alkalineearth metal component acts to neutralize the acidic materials used inthe preferred impregnation procedure for the platinum group and cadmiumcomponents. In fact, it is preferred to add the platinum group, cadmiumand alkali or alkaline earth components to the carrier material, oxidizethe resulting composite in a wet air stream at a high temperature (i.e.typically about 600° to 1000° F.), then treat the resulting oxidizedcomposite with steam or a mixture of air and steam at a relatively hightemperature of about 600° to about 1050° F. in order to remove at leasta portion of any residual acidity and thereafter add the rheniumcarbonyl component. Typically, the impregnation of the carrier materialwith this component is performed by contacting the carrier material witha solution of a suitable decomposable compound or salt of the desiredalkali or alkaline earth metal. Hence, suitable compounds include thealkali or alkaline earth metal halides, nitrates, acetates, carbonates,phosphates, and the like compounds. For example, excellent results areobtained by impregnating the carrier material with an aqueous solutionof chloroplatinic acid, lithium nitrate or potassium nitrate and nitricacid. Ordinarily, the amount of alkali or alkaline earth component isselected to produce a composite having an atomic ratio of alkali metalor alkaline earth metal to platinum group metal of about 5:1 to about100:1 or more, with the preferred range being about 10:1 to about 75:1.

After the platinum group component, manganese component and optionalalkali or alkaline earth component are combined with the porous carriermaterial, the resulting metals-containing carrier material willgenerally be dried at a temperature of about 200° F. to about 600° F.for a period of typically about 1 to about 24 hours or more andthereafter oxidized at a temperature of about 600° F. to about 1100° F.in an air or oxygen atmosphere for a period of about 0.5 to about 10 ormore hours effective to convert substantially all of the platinum group,manganese and alkali or alkaline earth components to the correspondingoxide forms. When acidic materials are used in incorporating thesemetallic components, best results are ordinarily achieved when theresulting oxidized composite is subjected to a high temperaturetreatment with steam or with a mixture of steam and a diluent gas suchas air or nitrogen either during or after this oxidation step in orderto remove as much as possible of the undesired acidic components such ashalogen and thereby prepare a substantially halogen-free,metals-containing oxidized carrier material. It is to be noted that itis essential that conditions used in this acidic component strippingstep be very carefully chosen to avoid any possibility of sintering oragglomerating the platinum group component.

A critical feature of the present invention involves subjecting theresulting oxidized, platinum group metal--and manganese--containing, andtypically alkali or alkline earth metal-containing carrier material to asubstantially water-free reduction step before the incorporation of therhenium component by means of the rhenium carbonyl reagent. Theimportance of this reduction step comes from my observation that when anattempt is made to prepare the instant catalytic composite without firstreducing the platinum group component, no significant improvement in theplatinum-rhenium-manganese catalyst system is obtained; put another way,it is my finding that it is essential for the platinum group componentto be well dispersed in the porous carrier material in the elementalmetallic state prior to incorporation of the rhenium component by theunique procedure of the present invention in order for synergisticinteraction of the rhenium carbonyl with the dispersed platinum groupmetal to occur according to the theories that I have previouslyexplained in my prior application Ser. No. 943,492. Accordingly, thisreduction step is designed to reduce substantially all of the platinumgroup component to the elemental metallic state and to assure arelatively uniform and finely divided dispersion of this metalliccomponent throughout the porous carrier material. Preferably, asubstantially pure and dry hydrogen-containing stream (by use of theword "dry" I mean that it contains less then 20 vol. ppm. water andpreferably less than 5 vol. ppm. water) is used as the reducing agent inthis step. The reducing agent is contacted with the oxidized, platinumgroup metal- and manganese-containing carrier material at conditionsincluding a reduction temperature of about 450° F. to about 1200° F. fora period of about 5.0 to about 10 or more hours selected to reducesubstantially all of the platinum group component to the elementalmetallic state. Once this condition of finely divided dispersed platinumgroup metal in the porous carrier material is achieved, it is importantthat environments and/or conditions that could disturb or change thiscondition be avoided; specifically, I much prefer to maintain thefreshly reduced carrier material containing the platinum group metalunder a blanket of inert gas to avoid any possibility of contaminationof same either by water or by oxygen.

A third essential ingredient of the present attenuated superactivecatalytic composite is a rhenium component which I have chosen tocharacterize as a pyrolyzed rhenium carbonyl component in order toemphasize that the rhenium moiety of interest in my invention is therhenium produced by decomposing a rhenium carbonyl in the presence of afinely divided dispersion of a platinum group metal and in the absenceof materials such as oxygen or water which could interfere with thedesired interaction of the rhenium carbonyl component with the platinumgroup metal component. In view of the fact that all of the rheniumcontained in a rhenium carbonyl compound is present in the elementalmetallic state, an essential requirement of my invention is that theresulting reaction product of the rhenium carbonyl compound or complexwith the platinum group metal--and manganese--loaded carrier material isnot subjected to conditions which could in any way interfere with themaintenance of the rhenium moiety in the elemental metallic state;consequently, avoidance of any conditions which would tend to cause theoxidation of any portion of the rhenium ingredient or of the platinumgroup ingredient is a requirement for full realization of thesynergistic interaction enabled by the present invention. This rheniumcomponent may be utilized in the resulting composite in any amount thatis catalytically effective with the preferred amount typicallycorresponding to about 0.01 to about 5 wt. % thereof, calculated on anelemental rhenium basis. Best results are ordinarily obtained with about0.05 to about 1 wt. % rhenium. The traditional rule for rhenium-platinumcatalyst systems that best results are achieved when the amount of therhenium component is set as a function of the amount of the platinumgroup component also hold for my composition; specifically, I find bestresults are obtained with a rhenium to platinum group metal atomic ratioof about 0.1:1 to about 10:1, with an especially useful range comprisingabout 0.2:1 to about 5:1 and with superior results achieved at an atomicratio of rhenium to platinum group metal of about 1:1.

The rhenium carbonyl ingredient may be reacted with the reduced platinumgroup metal--and manganese--containing porous carrier material in anysuitable manner known to those skilled in the catalyst formulation artwhich results in relatively good contact between the rhenium carbonylcomplex and the platinum group component contained in the porous carriermaterial. One acceptable procedure for incorporating the rheniumcarbonyl compound into the composite involves sublimating the rheniumcarbonyl complex under conditions which enable it to pass into the vaporphase without being decomposed and thereafter contacting the resultingrhenium carbonyl sublimate with the platinum group metal--andmanganese--containing porous carrier material under conditions designedto achieve intimate contact of the carbonyl reagent with the platinumgroup metal dispersed on the carrier material. Typically, this procedureis performed under vacuum at a temperature of about 70° to about 250° F.for a period of time sufficient to react the desired amount of rheniumcarbonyl complex with the carrier material. In some cases an inertcarrier gas such as nitrogen can be admixed with the rhenium carbonylsublimate in order to facilitate the intimate contacting of same withthe platinum--and manganese--loaded porous carrier material. Aparticularly preferred way of accomplishing this rhenium carbonylreaction step is an impregnation procedure wherein the platinum--andcadmium--loaded porous carrier material is impregnated with a suitablesolution containing the desired quantity of the rhenium carbonylcomplex. For purposes of the present invention, organic solutions arepreferred, although any suitable solution may be utilized as long as itdoes not interact with the rhenium carbonyl complex and causedecomposition of same. Obviously, the organic solution should beanhydrous in order to avoid detrimental interaction of water with therhenium carbonyl complex. Suitable solvents are any of the commonlyavailable organic solvents such as one of the available ethers,alcohols, ketones, aldehydes, paraffins, naphthenes and aromatichydrocarbons, for example, acetone, acetyl acetone, benzaldehyde,pentane, hexane, carbon tetrachloride, methyl isopropyl ketone, benzene,n-butylether, diethyl ether, ethylene glycol, methyl isobutyl ketone,diisobutylketone and the like organic solvents. Best results areordinarily obtained when the solvent is acetone; consequently, thepreferred impregnation solution is rhenium carbonyl complex dissolved inanhydrous acetone. The rhenium carbonyl complex suitable for use in thepresent invention may be either the pure rhenium carbonyl itself or asubstituted rhenium carbonyl such as the rhenium carbonyl halidesincluding the chlorides, bromides, and iodides and the like substitutedrhenium carbonyl complexes. After impregnation of the carrier materialwith the rhenium carbonyl component, it is important that the solvent beremoved or evaporated from the catalyst prior to decomposition of therhenium carbonyl component by means of the hereinafter describedpyrolysis step. The reason for removal of the solvent is that I believethat the presence of organic materials such as hydrocarbons orderivatives of hydrocarbons during the rhenium carbonyl pyrolysis stepis highly detrimental to the synergistic interaction associated with thepresent invention. This solvent is removed by subjecting the rheniumcarbonyl impregnated carrier material to a temperature of about 100° F.to about 250° F. in the presence of an inert gas or under a vacuumcondition until substantially no further solvent is observed to come offthe impregnated material. In the preferred case where acetone is used asthe impregnation solvent, this drying of the impregnated carriermaterial typically takes about one half hour at a temperature of about225° F. under moderate vacuum conditions.

After the rhenium carbonyl component is incorporated into theplatinum-and-manganese-loaded porous carrier material, the resultingcomposite is, pursuant to the present invention, subjected to pyrolysisconditions designed to decompose substantially all of the rheniumcarbonyl material, without oxidizing either the platinum group or thedecomposed rhenium carbonyl component. This step is preferably conductedin an atmosphere which is substantially inert to the rhenium carbonylcomplex such as in a nitrogen or noble gas-containing atmosphere.Preferably, this pyrolysis step takes place in the presence of asubstantially pure and dry hydrogen stream. It is of course within toconduct the scope of the present invention to conduct the pyrolysis stepunder vacuum conditions. It is much preferred this step in thesubstantial absence of free oxygen and substances that could yield freeoxygen under the conditions selected. Likewise, it is clear that bestresults are obtained when this step is performed in the total absence ofwater and of hydrocarbons and other organic materials. I have obtainedbest results in pyrolyzing rhenium carbonyl while using an anhydroushydrogen stream at pyrolysis conditions including a temperature of about300° F. to about 900° F. or more, preferably about 400° F. to about 750°F., a gas hourly space velocity of about 250° to about 1500 hr.⁻¹ for aperiod of about 0.5 to about 5 or more hours until no further evolutionof carbon monoxide is noted. After the rhenium carbonyl component hasbeen pyrolyzed, it is a much preferred practice to maintain theresulting catalytic composite in an inert environment (i.e. a nitrogenor the like inert gas blanket) until the catalyst is loaded into areaction zone for use in the dehydrogenation of hydrocarbons.

The resulting pyrolyzed catalytic composite may, in some cases, bebeneficially subjected to a presulfiding step designed to incorporate inthe catalytic composite from about 0.01 to about 1 wt. % sulfurcalculated on an elemental basis. Preferably, this presulfidingtreatment takes place in the presence of hydrogen and a suitabledecomposable sulfur-containing compound such as hydrogen sulfide, lowermolecular weight mercaptans, organic sulfides, etc. Typically, thisprocedure comprises treating the pyrolyzed catalyst with a sulfiding gassuch as a mixture of hydrogen and hydrogen sulfide containing 1 to about10 moles of hydrogen per mole of hydrogen sulfide at conditionssufficient to effect the desired incorporation of sulfur, generallyincluding a temperature ranging from about 50° F. to about 1000° F. Itis generally a preferred practice to perform this presulfiding stepunder substantially water-free and oxygen-free conditions. It is withinthe scope of the present invention to maintain or achieve the sulfidedstate of the present catalyst during use in the dehydrogenation ofhydrocarbons by continuously or periodically adding a decomposablesulfur-containing compound, selected from the above-mentionedhereinbefore, to the reactor containing the superactive catalyst in anamount sufficient to provide about 1 to 500 wt. ppm., preferably about 1to about 20 wt. ppm. of sulfur, based on hydrocarbon charge. Accordingto another mode of operation, this sulfiding step may be accomplishedduring the pyrolysis step by utilizing a rhenium carbonyl reagent whichhas a sulfur-containing ligand or by adding H₂ S to the hydrogen streamwhich is preferably used therein.

According to the method of the present invention, the dehydrogenatablehydrocarbon is contacted with the attenuated superactive multimetalliccatalytic composite described above in a dehydrogenation zone maintainedat dehydrogenation conditions. This contacting may be accomplished byusing the catalyst in a fixed bed system, a moving bed system, afluidized bed system, or in a batch type operation; however, in view ofthe danger of attrition losses of the valuable catalyst and ofwell-known operational advantages, it is preferred to use a fixed bedsystem. In this system, the hydrocarbon feed stream is preheated by anysuitable heating means to the desired reaction temperature and thenpassed into a dehydrogenation zone containing a fixed bed of thecatalyst previously characterized. It is, of course, understood that thedehydrogenation zone may be one or more separate reactors with suitableheating means therebetween to insure that the desired conversiontemperature is maintained at the entrace to each reactor. It is also tobe noted that the reactants may be contacted with the catalyst bed ineither upward, downward, or radial flow fashion with the latter beingpreferred. In addition, it is to be noted that the reactants may be inthe liquid phase, a mixed liquid-vapor phase, or a vapor phase when theycontact the catalyst, with best results obtained in the vapor phase.

Although hydrogen is the preferred diluent for use in the subjectdehydrogenation method, in some cases other art-recognized diluents maybe advantageously utilized, either individually or in admixture withhydrogen or each other, such as steam, methane, ethane, carbon dioxide,and the like diluents. Hydrogen is preferred because it serves thedual-function of not only lowering the partial pressure of thedehydrogenatable hydrocarbon, but also of suppressing the formation ofhydrogen-deficient, carbonaceous deposits on the catalytic composite.Ordinarily, hydrogen is utilized in amounts sufficient to insure ahydrogen to hydrocarbon mole ratio of about 1:1 to about 20:1, with bestresults obtained in the range of about 1.5:1 to about 10:1. The hydrogenstream charged to the dehydrogenation zone will typically be recycledhydrogen obtained from the effluent stream from this zone after asuitable hydrogen separation step. As explained in my prior applicationSer. No. 943,492, a highly preferred mode of operation of the instantdehydrogenation method is in a substantially water-free environment;however, when utilizing hydrogen in the instant method, improvedselectivity results are obtained under certain limited circumstances, ifwater or a water-producing substance (such as an alcohol, ketone, ether,aldehyde, or the like oxygen-containing decomposable organic compound)is added to the dehydrogenation zone in an amount calculated on thebasis of equivalent water, corresponding to about 1 to about 5,000 wt.ppm. of the hydrocarbon charge stock, with about 1 to 1,000 wt. ppm. ofwater giving best results. This water addition feature may be used on acontinuous or intermittent basis to regulate the activity andselectivity of the instant catalyst.

Regarding the conditions utilized in the method of the presentinvention, these are generally selected from the dehydrogenationconditions well-known to those skilled in the art for the particulardehydrogenatable hydrocarbon which is charged to the process. Morespecifically, suitable conversion temperatures are selected from therange of about 700° to about 1300° F. with a value being selected fromthe lower portion of this range for the more easily dehydrogenatedhydrocarbons such as the long chain normal paraffins and from the highportion of this range for the more difficultly dehydrogenatedhydrocarbon such as propane, butane and the like hydrocarbons. Forexample, for the dehydrogenation of C₆ to C₃₀ normal paraffins, bestresults are ordinarily obtained at a temperature of about 800° to about950° F.; on the other hand, for the dehydrogenation of propane, bestresults are usually achieved at a temperature of about 1150° F. to 1250°F. The pressure utilized is ordinarily selected at a value which is aslow as possible consistent with the maintenance of catalyst stabilityand is usually about 0.1 to about 10 atmospheres with best resultsordinarily obtained in the range of about 0.5 to about 3 atmospheres. Inaddition, a liquid hourly space velocity (calculated on the basis of thevolume amount, as a liquid, of hydrocarbon charged to thedehydrogenation zone per hour divided by the volume of the catalyst bedutilized) is selected from the range of about 1 to about 40 hr.⁻¹, withbest results for the dehydrogenation of long-chain normal paraffinstypically obtained at a relatively high space velocity of about 20 to 35hr.⁻¹ and for the more refractory paraffins at a space velocity of about3 to about 10 hr.⁻¹.

Regardless of the details concerning the operations of thedehydrogenation step, an effluent stream will be withdrawn therefrom.This effluent will usually contain unconverted dehydrogenatablehydrocarbons, hydrogen, and products of the dehydrogenation reaction.This stream is typically cooled and passed to a hydrogen-separating zonewherein a hydrogen-rich vapor phase is allowed to separate from thehydrocarbon-rich liquid phase. In general, it is usually desired torecover the unreacted dehydrogenatable hydrocarbon from thishydrocarbon-rich liquid phase in order to make the dehydrogenationprocess economically attractive. This recovery operation can beaccomplished in any suitable manner known to the art such as by passingthe hydrocarbon-rich liquid phase through a bed of suitable adsorbentmaterial which has the capability to selectively retain thedehydrogenated hydrocarbons contained therein or by contacting same witha solvent having a high selectivity for the dehydrogenated hydrocarbon,or by a suitable fractionation scheme where feasible. In the case wherethe dehydrogenated hydrocarbon is a mono-olefin, suitable adsorbentshaving this capability are activated silica gel, activated carbon,activated alumina, various types of specially prepared zeoliticcrystalline aluminosilicates, molecular sieves, and the like adsorbents.In another typical case, the dehydrogenated hydrocarbons can bespearated from the unconverted dehydrogenatable hydrocarbons byutilizing the inherent capability of the dehydrogenated hydrocarbons toeasily enter into several well-known chemical reactions such asalkylation, oligomerization, halogenation, sulfonation, hydration,oxidation, and the like reactions. Irrespective of how thedehydrogenated hydrocarbons are separated from the unreactedhydrocarbons, a stream containing the unreacted dehydrogenatablehydrocarbons will typically be recovered from this hydrocarbonseparation step and recycled to the dehydrogenation step. Likewise, thehydrogen phase present in the hydrogen-separating zone will be withdrawntherefrom, a portion of it vented from the system in order to remove thenet hydrogen make, and the remaining portion is typically recycledthrough suitable compressing means to the dehydrogenation step in orderto provide diluent hydrogen therefor.

In a preferred embodiment of the present invention wherein long chainnormal paraffin hydrocarbons are dehydrogenated to the correspondingnormal mono-olefins, a preferred mode of operation of this hydrocarbonrecovery step involves an alkylation reaction. In this mode, thehydrocarbon-rich liquid phase withdrawn from the hydrogen-separatingzone is combined with a stream containing an alkylatable aromatic andthe resulting mixture passed to an alkylation zone containing a suitablehighly acid catalyst such as an anhydrous solution of hydrogen fluoride.In the alkylation zone the mono-olefins react with alkylatable aromaticwhile the unconverted normal paraffins remain substantially unchanged.The effluent stream from the alkylation zone can then be easilyseparated, typically by means of a suitable fractionation system, toallow recovery of the unreacted normal paraffins. The resulting streamof unconverted normal paraffins is then usually recycled to thedehydrogenation step of the present invention.

The following working examples are introduced to illustrate further thedehydrogenation method and the attentuated superactive multimetalliccatalytic composite of the present invention. These examples of specificembodiments of the present invention are intended to be illustrativerather than restrictive.

These examples are all performed in a laboratory scale dehydrogenationplant comprising a reactor, a hydrogen separating zone, heating means,cooling means, pumping means, compressing means, and the likeconventional equipment. In this plant, the feed stream containing thedehydrogenatable hydrocarbon is combined with a hydrogen-containing,substantially water-free, recycle gas stream and the resultant mixtureheated to the desired conversion temperature, which refers herein to thetemperature maintained at the inlet to the reactor. The heated mixtureis then passed into contact with the instant attenuated superactivemultimetallic catalyst which is maintained as a fixed bed of catalystparticles in the reactor. The pressures reported herein are recorded atthe outlet from the reactor. An effluent stream is withdrawn from thereactor, cooled, and passed into the hydrogen-separating zone wherein ahydrogen-containing gas phase separates from a hydrocarbon-rich liquidphase containing dehydrogenated hydrocarbons, unconverteddehydrogenatable hydrocarbons, and a minor amount of side products ofthe dehydrogenation reaction. A portion of the hydrogen-containing gasphase is recovered as excess recycle gas with the remaining portionbeing continuously recycled, after water addition as needed, throughsuitable compressing means to the heating zone as described above. Thehydrocarbon-rich liquid phase from the separating zone is withdrawntherefrom and subjected to analysis to determine conversion andselectivity for the desired dehydrogenated hydrocarbon as will beindicated in the Examples. Conversion numbers of the dehydrogenatablehydrocarbon reported herein are all calculated on the basis ofdisappearance of the dehydrogenatable hydrocarbon and are expressed inmole percent. Similarly, selectivity numbers are reported on the basisof moles of desired hydrocarbon produced per 100 moles ofdehydrogenatable hydrocarbon converted.

All of the catalysts utilized in these examples are prepared accordingto the following preferred method with suitable modification instoichiometry to achieve the compositions reported in each example.First, an alumina carrier material comprising 1/16 inch spheres havingan apparent bulk density of about 0.3 g/cc is prepared by: forming analumina hydroxyl chloride sol by dissolving substantially pure aluminumpellets in a hydrochloric acid solution, adding hexamethylenetetramineto the resulting alumina sol, gelling the resulting solution by droppingit into an oil bath to form spherical particles of an alumina hydrogel,aging, and washing the resulting particles with an ammoniacal solutionand finally drying, calcining, and steaming the aged and washedparticles to form spherical particles of a substantially halogen-freegamma-alumina containing substantially less than 0.1 wt. % combinedchloride. Additional details as to this method of preparing this aluminacarrier material are given in the teachings of U.S. Pat. No. 2,620,314.

A first aqueous impregnation solution containing permanganic acid isthen prepared. The alumina carrier material is thereafter admixed withthe impregnation solution. The amount of the manganese reagent containedin this impregnation solution is calculated to result in a finalcomposite containing the hereinafter specified amounts of manganese.This impregnation step is performed by adding the carrier materialparticles to the impregnation mixture with contant agitation. Inaddition, the volume of the solution is approximately the same as thebulk volume of the alumina carrier material particles so that all of theparticles are immersed in the impregnation solution. The impregnationmixture is maintained in contact with the carrier material particles fora period of about 1/2 to about 3 hours at a temperature of about 70° F.Thereafter, the temperature of the impregnation mixture is raised toabout 225° F. and the excess solution is evaporated in a period of about1 hour. The resulting dried impregnated particles are then subjected toan oxidation treatment in a dry air stream at a temperature of about975° F. and a GHSV of about 500 hr.⁻¹ for about 1/2 hour. This oxidationstep is designed to convert substantially all of the manganeseingredient to the corresponding manganese oxide or aluminate.

A second impregnation solution containing chloroplatinic acid, nitricacid and (when an alkali or alkaline earth component is used) eitherlithium nitrate or potassium nitrate is then prepared. Themanganese-containing alumina carrier material is thereafter admixed withthe impregnation solution. The amounts of the metallic reagentscontained in this impregnation solution are calculated to result in afinal composite containing the hereinafter specified amounts of themetallic components. In order to insure uniform dispersion of theplatinum component throughout the carrier material, the amount of nitricacid used in this impregnation solution is about 5 wt. % of the aluminaparticles. This impregnation step is performed by adding the carriermaterial particles to the impregnation mixture with constant agitation.In addition, the volume of the solution is approximately the same as thebulk volume of the alumina carrier material particles so that all of theparticles are immersed in the impregnation solution. The impregnationmixture is maintained a contact with the carrier material particles fora period of about 1/2 to about 3 hours at a temperature of about 70° F.Thereafter, the temperature of the impregnation mixture is raised toabout 225° F. and the excess solution is evaporated in a period of about1 hour. The resulting dried impregnated particles are then subjected toan oxidation treatment in a dry air stream at a temperature of about975° F. and a GHSV of about 500 hr.⁻¹ for about 1/2 hour. This oxidationstep is designed to convert substantially all of the metallicingredients to the corresponding oxide forms. The resulting oxidizedspheres are subsequently contacted in a steam-stripping step with an airstream containing about 1 to about 30% steam at a temperature of about800° to about 1000° F. for an additional period of about 1 to about 5hours in order to reduce any residual combined chloride to a value lessthan 0.5 wt. % and most preferably less than 0.2 wt. %. The oxidized andsteam-stripped spheres are thereafter subjected to a second oxidationstep with a dry air stream of 975° F. and a GHSV of 500 hr.⁻¹ for anadditional period of about 1/2 hour.

The resulting oxidized, stream-stripped carrier material particles arethen subjected to a dry reduction treatment designed to reducesubstantially all of the platinum component to the elemental state andto maintain a uniform dispersion of this component in the carriermaterial. This reduction step is accomplished by contacting theparticles with a hydrocarbon-free, dry hydrogen streamcontaining lessthan 5 vol. ppm. H₂ O at a temperature of about 1050° F., a pressureslightly above atmospheric, a flow rate of hydrogen through theparticles corresponding to a GHSV of about 400 hr.⁻¹ and for a period ofabout one hour.

Rhenium carbonyl complex, Re₂ (CO)₁₀, is thereafter dissolved in ananhydrous acetone solvent in order to prepare the rhenium carbonylsolution which is used as the vehicle for reacting rhenium carbonyl withthe carrier material containing the uniformly dispersed platinum andmanganese. The amount of the complex used is selected to result in afinished catalyst containing the hereinafter specified amount ofcarbonyl-derived rhenium metal. The resulting rhenium carbonyl solutionis then contacted under appropriate impregnation conditions with thereduced, platinum-and-manganese-containing alumina carrier materialresulting from the previously described reduction step. The impregnationconditions utilized are: a contact time of about one half to about threehours, a temperature of about 70° F. and a pressure of aboutatmospheric. It is important to note that this impregnation step isconducted under a nitrogen blanket so that oxygen is excluded from theenvironment and also this step was performed under anhydrous conditions.Thereafter, the acetone solvent is removed under flowing nitrogen at atemperature of about 175° F. for a period of about one hour. Theresulting dry rhenium carbonyl impregnated particles are then subjectedto a pyrolysis step designed to decompose the rhenium carbonylcomponent. This step involves subjecting the carbonyl impregnatedparticles to a flowing hydrogen stream at a first temperature of about230° F. for about one half hour at a GHSV of about 600 hr.⁻¹ and atatmospheric pressure. Thereafter, in the second portion of the pyrolysisstep, the temperature of the impregnated particles is raised to about575° F. for an additional interval of about one hour until the evolutionof CO was no longer evident. The resulting catalyst is then maintainedunder a nitrogen blanket until it is loaded into the reactor in thesubsequently described dehydrogenation test.

EXAMPLE I

The reactor is loaded with 100 cc of a catalyst containing, on anelemental basis, 0.375 wt. % platinum, 0.375 wt. % rhenium, 0.125 wt. %manganese, and less than 0.15 wt. % chloride. This corresponds to anatomic ratio of rhenium to platinum of 1.05:1 and of manganese toplatinum of 1.18:1. The feed stream utilized is commercial gradeisobutane containing 99.7 wt. % isobutane and 0.3 wt. % normal butane.The feed stream is contacted with the catalyst at a temperature of 975°F., a pressure of 10 psig., a liquid hourly space velocity of 4.0 hr.⁻¹,and a recycle gas to hydrocarbon mole ratio of 3:1. The dehydrogenationplant is lined-out at these conditions and a 20-hour test periodcommenced. The hydrocarbon product stream from the plant is continuouslyanalyzed by GLC (gas liquid chromatography) and a high conversion ofisobutane is observed with a high selectivity for isobutylene.

EXAMPLE II

The catalyst contains, on an elemental basis, 0.375 wt. % platinum, 0.5wt. % rhenium, 0.125 wt. % manganese, 0.6 wt. % lithium, and less than0.15 wt. % combined chloride. These amounts correspond to the followingatomic ratios: Re/Pt of 1.4:1, Mn/Pt of 1.18:1, and Li/Pt of 45:1. Thefeed stream is commercial grade normal dodecane. The dehydrogenationreactor is operated at a temperature of 850° F., a pressure of 10 psig.,a liquid hourly space velocity of 32 hr.⁻¹, and a recycle gas tohydrocarbon mole ratio of 5:1. After a line-out period, a 20-hour testperiod is performed during which the average conversion of the normaldodecane is maintained at a high level with a selectivity for normaldodecene of about 90%.

EXAMPLE III

The catalyst is the same as utilized in Example II. The feed stream isnormal tetradecane. The conditions utilized are a temperature of 830°F., a pressure of 20 psig., a liquid hourly space velocity of 32 hr.⁻¹,and a recycle gas to hydrocarbon mole ratio of 4:1. After a line-outperiod, a 20-hour test shows an average conversion of about 12%, and aselectivity for normal tetradecene of about 90%.

EXAMPLE IV

The catalyst contains, on an elemental basis, 0.2 wt. % platinum, 0.2wt. % rhenium, 0.1 wt. % manganese and 0.4 wt. % lithium, with combinedchloride being less than 0.2 wt. %. The pertinent atomic ratios are:Re/Pt of 1.05:1, Mn/Pt of 1.78:1 and Li/Pt of 56:1. The feed stream issubstantially pure cyclohexane. The conditions utilized are atemperature of 900° F., a pressure of 100 psig., a liquid hourly spacevelocity of 3.0 hr.⁻¹, and a recycle gas to hydrocarbon mole ratio of4:1. After a line-out period, a 20-hour test is performed with almostcomplete conversion of cyclohexane to benzene and hydrogen.

EXAMPLE V

The catalyst is the same as in Example IV. The feed stream is commercialgrade ethylbenzene. The conditions utilized are a pressure of 15 psig.,a liquid hourly space velocity of 32 hr.⁻¹, a temperature of 1010° F.,and a recycle gas to hydrocarbon mole ratio of 3:1. During a 20-hourtest period, 85% or more of equilibrium conversion of the ethylbenzeneis observed. The selectivity for styrene is about 90%.

EXAMPLE VI

The catalyst contains, on an elemental basis, about 0.75 wt. % platinum,about 0.8 wt. % rhenium, 0.25 wt. % manganese, about 0.6 wt. % lithiumand less than 0.2 wt. % chlorine. The relevant atomic ratios are: Re/Ptof 1.12:1, Mn/Pt of 1.18:1 and Li/Pt of 22.6:1. The charge stock issubstantially pure propane. The conditions utilized are: in inletreaction temperature of 1150° F., a pressure of 10 psig., a hydrogen topropane mole ratio of 2:1 and a liquid hourly space velocity of about 5hr.⁻¹. Results are: a conversion of propane of about 35% at aselectivity for propylene of about 85%.

It is intended to cover by the following claims all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in thecatalyst-formation art or in the hydrocarbon dehydrogenation art.

I claim as my invention:
 1. A nonacidic catalytic composite comprising acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous carrier material, containing a uniformdispersion of catalytically effective amounts of an alkali or alkalineearth component, a manganese component and a platinum group componentwhich is maintained in the elemental metallic state.
 2. A nonacidiccatalytic composite as defined in claim 1 wherein the composite containsthe components in amounts, calculated on an elemental basis,corresponding to about 0.01 to about 2 wt. % platinum group metal, about0.01 to about 5 wt. % rhenium, about 0.01 to about 5 wt. % manganese,and about 0.1 to about 5 wt. % alkali or alkaline earth metal.
 3. Anonacidic catalyst composite as defined in claim 1 wherein the porouscarrier material is a refractory inorganic oxide.
 4. A nonacidiccatalyst composite as defined in claim 3 wherein the refractoryinorganic oxide is alumina.
 5. A nonacidic catalyst composite as definedin claim 1 wherein the platinum group component is platinum.
 6. Anonacidic catalyst composite as defined in claim 1 wherein the platinumgroup component is palladium.
 7. A nonacidic catalyst composite asdefined in claim 1 wherein the platinum group component is rhodium.
 8. Anonacidic catalyst composite as defined in claim 1 wherein the platinumgroup component is iridium.
 9. A nonacidic catalyst composite as definedin claim 1 wherein the alkali or alkaline earth component is potassium.10. A nonacidic catalytic composite as defined in claim 1 wherein thealkali or alkaline earth component is lithium.
 11. A nonacidic catalystcomposite as defined in claim 1 wherein the catalytic composite is in asubstantially halogen-free state.
 12. A nonacidic catalyst composite asdefined in claim 1 wherein the composite contains, on an elementalbasis, about 0.05 to about 1 wt. % platinum group metal, about 0.05 toabout 1 wt. % rhenium, about 0.05 to about 1 wt. % manganese and about0.25 to about 3.5 wt. % alkali metal or alkaline earth metal.
 13. Anonacidic catalytic composite as defined in claim 1 wherein the metalscontents thereof is adjusted so that the atomic ratio of manganese toplatinum group metal is about 0.2:1 to about 3:1, the atomic ratio ofalkali or alkaline earth metal to platinum group metal is about 10:1 toabout 75:1 and the atomic ratio of rhenium, derived from the rheniumcarbonyl component, to platinum group metal is about 0.2:1 to about 5:1.